[Bldg-sim] LEED NC Submittal Template, Heating/Cooling Hours Loads Not Met

Dan Russell danr at engineeringinc.com
Thu Aug 21 11:12:06 PDT 2008

Brandon, I have been on the same page regarding this issue, and have
submitted for successful LEED certifications using those assumptions ...
until I read Addendum a to 90.1-2004, which adds the definition of
"unmet load hour" to Section 3.2.  The definition is:

unmet load hour: an hour in which one or more zones is outside of the
thermostat setpoint range.

Unfortunately this seems to clearly indicate the unmet load hour value
asked for refers to all zones at once.  

My previous assumptions to only consider the worst-case zone were based
on the example set forth by the USGBC's document titled "Example LEED-NC
v2.1 Energy & Atmosphere Credit 1 Submittal", which I referenced back
when I did my first LEED submittal in 2005.  This document is still
available from their server at the following address:


This document uses the following paragraph to demonstrate compliance
with the unmet load hour requirement:

"The worst-case zone in the budget case is a North classroom. This zone
is under-heated 40 hours out of the year in the Energy Cost Budget case
and 0 hours per year in the Design Energy Cost case. This is within the
50 hour per year limit required by ASHRAE 90.1-1999."

Now, if Addendum a were not used in any part as basis for LEED submittal
one could possibly argue using the quoted precedent above.  Granted, the
above precedent applied to the 1999 version of 90.1 and the 2.1 version
of LEED, but it seems to reasonable that the implications made there
should carry over until otherwise directed (as in Addendum a).
Furthermore, it is my opinion that 90.1-2004 (not including addendums)
does not clearly resolve the issue.  The ASHRAE technical committee must
have agreed, hence the inclusion of the new definition for "unmet load
hour" in Addendum a.

So, if Addendum a is not used, there may be a possibility to consider
unmet load hour only on a worst-zone basis.  However, if Addendum a is
used it seems clear that the unmet load hour applies to all zones at

Certainly larger project simulations with multiple zones will suffer
from this added definition.


 Dan Russell, EIT 

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Brandon
Sent: Thursday, August 21, 2008 11:22 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] LEED NC Submittal Template,Heating/Cooling Hours
Loads Not Met


"Table 1.3 -- Advisory Messages" of the LEED NC Submittal Template
requests "number of hours heating loads not met" and "number of hours
cooling loads not met".  We've taken a vote here in the office, and its
2-0 in favor of reporting the worst case zone as shown on the BEPS

But we have some lingering doubts... can anyone say definitively what
numbers are being asked to for here?  our runner-up in the voting was
the total of all zone hours out of throttling range -- however this
could easily exceed the limit of 300 hours on a large project with many

As 300 hours is less than 5% (3.4% actually) of 8760, we think that the
300 hours is "per zone", not a total limit for the entire project.  

Comments appreciated....
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